1. Field of the Invention
The present invention relates to a method for producing a target substance such as L-amino acids by fermentation using a microorganism. More precisely, the method for producing a target substance by fermentation uses xylose as a raw material.
2. Brief Description of the Related Art
Methods for producing target substances such as L-amino acids by fermentation using a bacterium include methods of using a wild-type bacterium (wild-type strain), methods of using an auxotrophic strain derived from a wild-type strain, methods of using a metabolic regulation mutant strain derived from a wild-type strain which is resistant to various drugs, methods of using a strain having properties of both auxotrophic strain and metabolic regulation mutant, and so forth.
For example, L-glutamic acid is mainly produced by fermentation using an L-glutamic acid-producing bacterium of the so-called coryneform bacteria belonging to the genus Brevibacterium, Corynebacterium or Microbacterium or a mutant strain thereof (refer to, for example, Akashi K. et al., Amino Acid Fermentation, Japan Scientific Societies Press, pp. 195-215, 1986). As methods for producing L-glutamic acid by using other strains, methods utilizing a microorganism belonging to the genus Bacillus, Streptomyces, Penicillium, or the like (refer to, for example, U.S. Pat. No. 3,220,929), methods utilizing a microorganism belonging to the genus Pseudomonas, Arthrobacter, Serratia, Candida, or the like (refer to, for example, U.S. Pat. No. 3,563,857), methods utilizing a microorganism belonging to the genus Bacillus, or Aerobacter aerogenes (currently Enterobacter aerogenes), or the like (refer to, for example, Japanese Patent Publication (Kokoku) No. 32-9393), methods utilizing a mutant strain of Escherichia coli (refer to, for example, Japanese Patent Laid-open (Kokai) No. 5-244970), and so forth are known. Furthermore, methods of producing L-glutamic acid using a microorganism belonging to the genus Klebsiella, Erwinia, Pantoea, or Enterobacter (refer to, e.g., Japanese Patent Laid-open No. 2000-106869, Japanese Patent Laid-open No. 2000-189169 and Japanese Patent Laid-open No. 2000-189175) have also been disclosed.
In recent years, recombinant DNA techniques have been used in the production of target substances by fermentation. For example, L-amino acid productivity of a bacterium is improved by enhancing expression of a gene encoding an L-amino acid biosynthetic enzyme (U.S. Pat. No. 5,168,056 and U.S. Pat. No. 5,776,736), or by enhancing uptake of a carbon source into the L-amino acid biosynthesis system (U.S. Pat. No. 5,906,925).
Conventional industrial production of substances by fermentation typically employ saccharides, i.e., glucose, fructose, sucrose, blackstrap molasses, starch hydrolysate, and so forth as a carbon source, but they are relatively expensive, and use of biomass raw materials derived from plants and the like has also advanced in recent years.
Although raw materials including edible portions such as starch and fats and oils are mainly used as such biomass raw materials at present, it is necessary to shift such biomass raw materials to those which include non-edible portions, specifically, cellulose, hemicellulose, lignin, and so forth in the future. Non-edible biomass such as cellulose and hemicellulose are converted into pentoses or hexoses via a pretreatment using heat or acid, and a saccharification treatment using a cellulase enzyme, and then they can be used as raw materials in fermentation (Japanese Patent Laid-open based on PCT application (Kohyo) No. 9-507386 and Japanese Patent Laid-open based on PCT application No. 11-506934). If mixed saccharides of pentoses or hexoses are used as the raw materials for amino acid fermentation etc., Escherichia coli preferentially assimilates glucose, and as a result, the phenomena of two-step proliferation (diauxy), delayed growth etc. have been observed (Nichols N. N. et al., Appl. Microbiol. Biotechnol., 2001 July, 56(1-2):120-125 and Gonzalez, R., Biotechnol. Prog., 2002 January-February, 18(1):6-20)
In Escherichia coli, a xylose assimilation pathway utilizing xylose isomerase encoded by the xylA gene and xylulokinase encoded by the xylB gene is known, and it is also known that L-amino acids can be produced from xylose by introducing that pathway into Escherichia coli or Corynebacterium glutamicum (Tao H. et al., J. Bacteriol., 2001 May, 183 (10):2979-2988, European Patent No. 1577396, Gopinath, V. et al., Appl. Microbiol. Biotechnol., 2011 Jul., 28).
It has also been reported that Caulobacter crescentus and Haloferax volcanii utilize a pathway of converting xylose into 2-ketoglutaric acid via xylonic acid in five steps, not using the conventionally known pathway as described above (Stephens, C. et al., J. Bacteriol., 2007 March, 189 (5):2181-2185). Moreover, examples of expression of that pathway in Escherichia coli are also known (Huaiwei, L et al., Bioresour Technol., 2011 Aug., 22, U.S. Pat. No. 7,923,226).